On 5/11/23 4:15 AM, Stefano Garzarella wrote:
The virtio-blk-vhost-vdpa driver in libblkio 1.3.0 supports the new
'fd' property. Let's expose this to the user, so the management layer
can pass the file descriptor of an already opened vhost-vdpa character
device. This is useful especially when the device can only be accessed
with certain privileges.
If the libblkio virtio-blk driver supports fd passing, let's always
use qemu_open() to open the `path`, so we can handle fd passing
from the management layer through the "/dev/fdset/N" special path.
Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
---
Notes:
v3:
- use qemu_open() on `path` to simplify libvirt code [Jonathon]
Thanks
The one drawback now is that it doesn't seem possible for libvirt to
introspect whether or not qemu supports passing an fd to the driver or
not. When I was writing my initial patch (before I realized that it was
missing fd-passing), I just checked for the existence of the
virtio-blk-vhost-vdpa device. But we actually need to know both that
this device exists and supports fd passing. As far as I can tell,
versions 7.2.0 and 8.0.0 include this device but won't accept fds.
Jonathon
block/blkio.c | 53 ++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 44 insertions(+), 9 deletions(-)
diff --git a/block/blkio.c b/block/blkio.c
index 0cdc99a729..6a6f20f923 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -672,25 +672,60 @@ static int blkio_virtio_blk_common_open(BlockDriverState
*bs,
{
const char *path = qdict_get_try_str(options, "path");
BDRVBlkioState *s = bs->opaque;
- int ret;
+ bool fd_supported = false;
+ int fd, ret;
if (!path) {
error_setg(errp, "missing 'path' option");
return -EINVAL;
}
- ret = blkio_set_str(s->blkio, "path", path);
- qdict_del(options, "path");
- if (ret < 0) {
- error_setg_errno(errp, -ret, "failed to set path: %s",
- blkio_get_error_msg());
- return ret;
- }
-
if (!(flags & BDRV_O_NOCACHE)) {
error_setg(errp, "cache.direct=off is not supported");
return -EINVAL;
}
+
+ if (blkio_get_int(s->blkio, "fd", &fd) == 0) {
+ fd_supported = true;
+ }
+
+ /*
+ * If the libblkio driver supports fd passing, let's always use qemu_open()
+ * to open the `path`, so we can handle fd passing from the management
+ * layer through the "/dev/fdset/N" special path.
+ */
+ if (fd_supported) {
+ int open_flags;
+
+ if (flags & BDRV_O_RDWR) {
+ open_flags = O_RDWR;
+ } else {
+ open_flags = O_RDONLY;
+ }
+
+ fd = qemu_open(path, open_flags, errp);
+ if (fd < 0) {
+ return -EINVAL;
+ }
+
+ ret = blkio_set_int(s->blkio, "fd", fd);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "failed to set fd: %s",
+ blkio_get_error_msg());
+ qemu_close(fd);
+ return ret;
+ }
+ } else {
+ ret = blkio_set_str(s->blkio, "path", path);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "failed to set path: %s",
+ blkio_get_error_msg());
+ return ret;
+ }
+ }
+
+ qdict_del(options, "path");
+
return 0;
}
